Low Cost ATM and the ATM Warren

The ATM Warren was a demonstration that ATM networks could be built as
cheaply as Ethernet networks. The essence of the Warren was to use only third-party
set up of calls between simple devices and switches, while maintaining fully-standard ATM
networking operation at all interfaces.

The Warren was an ATM sub-network composed of an arbitrary mesh of very
simple ATM switches and end stations and which is connected to the outside
ATM network at one or more points. The novel aspect was that switches and end
stations within the Warren were implementable entirely in hardware - i.e. they
required no microprocessors for signalling and management. All of the
signalling software for all the devices within the Warren were provided by one
or more proxy servers. The proxy servers are software entities situated on
one or more general-purpose computers connected to the external ATM network
outside the Warren.

Devices

A number of prototype devices were built under the sponsorship of Virata.
These were intended for the home. The home needs a low-cost network that
is multi-media capable. Both software and hardware devices were created.

Warren Switch

One of the first devices built was the 6 port Warren switch. This provided
six ports of ATM-25. It was designed by Daniel Gordon. Like all Warren devices, it
did not contain any microprocessors, but instead was controlled by a master controller
situated anywhere on the network. The Warren protocol allowed devices to keep in
touch with their controller, and this was implemented in hardware at the device end.

Two versions of the switch were designed. Although similar externally, the second version
had two levels of priority for FIFO queuing and a 32 kbyte buffer store for bursty traffic.
SPEC.

Warren Microphone

The very first devices buit were these microphones. They took power
over the ATM-25 RJ45 connection and generated a continuous stream
of cells.

The physical design, when cased, was meant to resemble a hand-held mic, like an SM58.
SPEC.

Warren CD Player

The Warren CD players were created by placing an ATM-25 line card in the back
of a commercial CD player.

The services available over the network were sourcing music and
control of the device using an ATM encoding of the infra-red remote control. Also, the
infra-red received at the device's local receiver could be decoupled from local control
and relayed over the network.

Warren Telephone: 1997-98

This was probably the first telephone handset/instrument to directly connect to a
packet-switched data network. It was a direct decendent of the Ring
Phones connected to the original Cambridge Ring as part of
the ISLAND
project and a similar project at Xerox PARC. The Ring Phones used a 19 inch rack, whereas the Warren
phone, like the
later ORL Broadband
Phone and CISCO 7941 IP phone, connected to the network using a
packet-switched data link. Between the Ring Phone and the Warren Phone
there was a whole generation of N-ISDN phones that, while digital, still
used circuit switching.

The Warren telephones were created by replacing the PCB inside
a standard telephone set with a new digital card. The card supports
ATM-25 on unshielded twisted-pair (UTP) or on plastic optical fiber (POF).

The telephones provided all the usual functions of a telephone
handset. There was no state or microprocessor in the phone. Every
operation was relayed directly over the network interface. Each button
push and release caused an ATM cell to be sent. Similarly, off hook
status, ringing and tone generation were marked and enabled by a continuous
stream of cells, instead of having specific cells to mark
the start and stop these states. Such an approach avoided any state
needing to be stored inside the phone.

Competition

The competition to the Warren was Switched Ethernet. Ethernet
could not support QoS but did not suffer from `badput' during
congestion where the remains of a datagram were shipped over the
network, only to fail in reassembly. Also, the complexity of ATM
protocols defined for telecoms use meant that full-featured switches,
like the Virata 12+12 shown below, were more complex than Ethernet
alternatives for the workgroup. The Warren was primarily a
demonstration that this did not have to be the case:
the software complexity could be selectively
deployed at any point, providing a seamless, interoperable spectrum
between none and the full CCITT stacks.

These workgroup ATM-25 switches contained their own microprocessor and a good deal
more silicon. The Warren switch pictured above is resting on the Virata 12x12 switch.
The Virata switch could control a number of Warren switches. Indeed, many thousands
of Warren devices could be interconnected and run of one controller if desired.

In the end, the real competition was switched Ethernet. Today we are learning
how to achieve QoS over Ethernet and in the Internet in general. ATM's reduced complexity
owing to using fixed-length cells was a chimera that soon became irrelevant with advances in VLSI,
and its provision for in-band QoS support mechanisms, such as priority, based on
connection-oriented virtual-circuits, is now less favoured than on-the-fly fairness
algorithms, implemented in routers that identify the flows for themselves.